Webbing Take-Up Device Load Limiting Clutch Mechanism
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Solution Overview
Problem
Existing webbing take-up devices face issues with stabilizing the load imparted to the connection-disconnection mechanism between a motor and a spool, leading to reduced durability of the clutch due to varying centrifugal forces from clutch weights, which deploy regardless of motor rotation direction and speed.
Innovation Solution
A webbing take-up device is designed with a load limiting portion to restrict the force imparted to the connection-disconnection mechanism, featuring a dual clutch system with different speed reduction ratios for forward and reverse rotations, and a spring-biased spool for stable webbing take-up, along with a lever and clutch spring mechanism to stabilize the engagement load.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If clutch weights are used to transmit motor rotation to the spool, then the spool can rotate in the take-up direction, but the load imparted to the connection-disconnection mechanism varies with revolution speed, reducing stability
Solution Approach 1:
The patent introduces a load limiting portion that changes the operational parameters of the clutch weights by limiting their revolution speed. This prevents the clutch weights from rotating too fast, thereby stabilizing the centrifugal force they generate and the load they impart to the connection-disconnection mechanism, resolving the contradiction between reliability and load consistency.
2Reliability
If clutch weights deploy based on centrifugal force, then the connection-disconnection mechanism can engage, but the clutch weights deploy regardless of motor rotation direction, causing unnecessary deployments
Solution Approach 1:
The patent employs asymmetric design in the connection-disconnection mechanism where the engagement condition is different for forward and reverse rotation. The clutch weights are configured to deploy only when the motor rotates in the reverse direction, creating an asymmetric response that prevents unnecessary deployments during forward rotation while ensuring reliable engagement when needed.
3Productivity
If the connection-disconnection mechanism receives full force from deploying clutch weights, then rotation transmission is efficient, but the durability of the mechanism decreases due to excessive load
Solution Approach 1:
The patent incorporates a load limiting portion that acts as a pre-designed load management element. This portion limits the maximum force that can be transmitted from the clutch weights to the connection-disconnection mechanism, providing beforehand cushioning that protects the mechanism from excessive loads while maintaining sufficient transmission efficiency for normal operation.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution stabilizes the load on the connection-disconnection mechanism, enhances the durability of the clutch, and ensures efficient webbing take-up and storage by controlling clutch weight deployment, thereby improving the overall performance and reliability of the webbing take-up device.
Implementation Method 1
a clutch weight that is rotated by the output shaft and that deploys as a result of its own centrifugal force
Data Source
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AI summary
A webbing take-up device includes a spool and a spiral spring that biases the spool in a take-up direction and a motor provided with an output shaft. The webbing take-up device further includes a first clutch that transmits forward direction rotation of the output shaft to the spool, rotating the spool in the take-up direction. The webbing take-up device further includes a second clutch including: weights that are rotated by the output shaft and that open out under their own centrifugal force; a connection-disconnection mechanism that receives force from the weights opening out and connects so as to enable rotation of the output shaft to be transmitted to the spool; and projection portions serving as load limiting portions that limit the load imparted to the connection-disconnection mechanism so as not to become a specific value or greater.